AN EXPERIMENTAL AND THEORETICAL-STUDY OF THE ELECTRONIC-STRUCTURE OF ZINC THIOPHENOLATE-CAPPED CLUSTERS

The electronic structure of a series of thiophenolate-capped ionic/neu tral clusters ([Zn(SPh)(4)](2-)(1); [Zn-4(mu(2)-SPh)(6)(SPh)(4)](2-)(2 ); Zn-10(mu(3)-S)(4)(mu(2)-SPh)(12) (3); and [Zn-10(mu(3)-S)(4)(mu(2)- SPh)(12)(SPh)(4)](4-)(4), Ph = phenyl), indicated as supertetrahedral fragments and possible molecular models of cubic ZnS, has been investi gated by coupling density functional calculations to UV electronic and X-ray photoelectron (XP) spectroscopy. Theoretical outcomes indicate that, on passing from the tetrametallic to the decametallic clusters, there is a modification in the nature of the outermost occupied and lo wermost unoccupied molecular orbitals. Actually, both in 1 and in 2 th e frontier orbitals are delocalized and mainly composed of the S 3p pa irs strongly mixed with the Ph pi levels (the HOMOs) and of the linear combinations of Ph pi orbitals, the LUMOs. At variance to that, in 3 and 4 both the HOMO and LUMO are highly localized, the former on mu(3 )-S atoms occupying C-3 nu coordinatively unsaturated tetrahedral posi tions and the latter on peripheral Zn atoms. The nature of the electro nic levels involved in the UV absorption bands is discussed, and the a greement between theory and experiment is satisfactory. Neither experi mental nor theoretical electronic excitation energies are influenced b y the cluster size. Moreover, XPS data match quite well variations of the Zn and S gross atomic charges along the series. The different Zn-S bonding scheme characterizing terminal, mu(2)-bridging, and mu(3)-pyr amidal S atoms allows a rationalization of the cluster behavior in sol ution. Along the investigated series, the only species reasonably mimi cking both the structural arrangement and the electronic structure of the solid ZnS is Zn10(mu(3)-S)(4)(mu(2)-SPh)(12), which can be conside red a molecular model of ZnS nonpolar surfaces.